Ōryoku Maru was a Japanese passenger cargo ship which was commissioned by the Imperial Japanese Navy during World War II as a troop transport and prisoner of war (POW) transport ship. Japanese POW transport ships are often referred to as hell ships, due to their notoriously unpleasant conditions and the many deaths that occurred on board. In December 1944, the ship was bombed by American aircraft, killing 200 Allied POWs. Hundreds more died in the months that followed.